1. Field of the Invention
The present invention relates to a clock device, a clock system and a time measuring method which appropriately clock the pass time of a moving body, e.g., the time of an athlete while preventing false detection of an electromagnetic field or the like.
2. Description of the Related Art
Recently, an attempt of measuring (clocking) goal times of individual athletes has been made in marathons. For example, a measuring system, which has a bar-code printed on the number cloth of a runner, and measures the goal time of an individual runner based on a time when the bar-code of the runner who has crossed the goal line is read through a reader, is in practical use.
Nowadays, to measure a competition time including a pass time at a halfway clock point, an attempt of measuring the competition time of an individual runner by a non-contact scheme has been made. For example, a measuring system which causes an athlete to hold a tag transmitter (wireless tag or the like), and measures a competition time through the tag transmitter is developed, and the operational test thereof or the like is attempted for practical usage.
As an example, Unexamined Japanese Patent Application KOKAI Publication No. 2006-47263 (P11 to P25, and FIG. 1) discloses a technology which specifies a measuring time (competition time) by causing a wireless tag, which includes a clock unit and is held by an athlete, to detect a predetermined electromagnetic field.
According to the foregoing technology, as shown in FIG. 9A in detail, a loop coil formed in a shape like figure of 8 is disposed on a course (clock point) through which an athlete runs to generate an electromagnetic field. That is, an electromagnetic field shown in FIG. 9B is generated on the loop coil. The electromagnetic field includes an additional side lobe SL in addition to a main lobe ML used for measurement.
As the athlete reaches the clock point (loop coil) and moves on such an electromagnetic field, the wireless tag detects a point b (trigger point) shown in FIG. 9B through the change of the electromagnetic field, thus measuring a competition time. Information on the measured competition time and the like is transmission data from the wireless tag to a receiver.
According to the foregoing technology, the change of the electromagnetic field (more specifically, detection of a point where the polarity of an electromagnetic field intensity changes) is set as a condition of detecting a trigger point in the electromagnetic field shown in FIG. 9B.
However, in the vicinity of a point a where detection of the electromagnetic field is started, the signal level of the electromagnetic field becomes unstable, so that the wireless tag catches the change, resulting in false detection of a trigger point. Therefore, in practice, an operation of detecting a trigger point is started after a predetermined time has passed from first detection of the electromagnetic field. That is, the wireless tag is set to have a non-detection time, and the operation of detecting a trigger point is started after the non-detection time passes from when the electromagnetic field is detected at first in the vicinity of the point a, so that the point b is detected as the trigger point.
However, every time the abilities of runners (moving speeds on the loop coil) differ, e.g., cases like an international competition and a civic competition, and a men's competition and a women's competition, it is necessary to set the non-detection time in accordance with the abilities of the runners. This is extremely bothersome, thus the non-detection time may be set falsely, and there is a possibility such that setting itself is not carried out at all.
If the electromagnetic field to be generated on the loop coil is not appropriate (too large) and the trigger level of the wireless tag is not appropriate (too low), the side lobe LS may be detected. In this case, even if the non-detection time is set appropriately, the start of the detection operation is so fast that the wireless tag detects the change of the electromagnetic field other than the point b, resulting in false detection of a trigger point.
Further, in a relay competition like a marathon relay race, a person who arrives a point (a runner who has run a previous interval) and a person who departs from the point (a runner who is about to run a current interval) may run on the same loop coil in receiving a cross brace or a baton. At this time, wireless tags of both runners respectively perform transmission of a competition time.
In this case, only the competition time of the person who arrives the point is valid, and it is necessary to discard the competition time transmission data from the person who departs the point. Accordingly, it is necessary to register identification information or the like for identifying the wireless tag of the person who arrives a point beforehand in a reception-side processing device.
The wireless tag of the departing person ever performs unnecessary transmission, and due to a collision with the unnecessary transmission or the like, an adverse effect may be given when the wireless tag of the arriving person transmits a competition time.